Methods and apparatus for treating disc herniation and preventing the extrusion of interbody bone graft

ABSTRACT

Methods and apparatus for treating disc herniation provide a conformable device which assumes a first shape associated with insertion and a second shape or expanded shape to occlude the defect which typically follows partial discectomy. The device may take different forms according to the invention, including patches size to cover the defect or plugs adapted to fill the defect. In a preferred embodiment, however, the device is a gel or other liquid or semi-liquid which solidifies to occlude the defect from within the body of the disc itself. In another preferred embodiment, a mesh screen is collapsed into an elongated form for the purposes of insertion, thereby minimizing the size of the requisite incision while avoiding delicate surrounding nerves. Such a configuration also permits the use of instrumentation to install the device, including, for example, a hollow tube or sheath adapted to hold the collapsed screen, and a push rod to expel the collapsed device out of the sheath for use in occluding the disc defect. A device according to the invention may further include one or more anchors to assist in permanently affixing the device with respect to the defect.

REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 11/443,789,filed May 30, 2006, which is a continuation of U.S. patent applicationSer. No. 10/630,445, filed Jul. 30, 2003, which is a continuation ofU.S. patent application Ser. No. 09/638,241, filed Aug. 14, 2000, whichis a continuation-in-part of International Patent Application No.PCT/US00/14708, filed May 30, 2000, which is a continuation-in-part ofand claims the benefit under 35 USC §119 of U.S. patent application Ser.No. 09/322,516, filed May 28, 1999, now U.S. Pat. No. 6,245,107. The'241 application also claims priority from U.S. Provisional PatentApplication Ser. No. 60/148,913, filed Aug. 13, 1999. The entire contentof each application and patent is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to the prosthetic appliances and, inparticular, to devices for occluding intervertebral disc defects andinstrumentation associated with introducing such devices.

BACKGROUND OF THE INVENTION

Several hundred thousand patients undergo disc operations each year.Approximately five percent of these patients will suffer recurrent discherniation, which results from a void or defect which remains in theouter layer (annulus fibrosis) of the disc after surgery involvingpartial discectomy.

Reference is made to FIG. 1A, which illustrates a normal disc as viewedfrom the feet of a patient up toward the head. The nucleus pulposus 102is entirely surrounded by the annulus fibrosis 104 in the case ofhealthy anatomy. Also shown in this cross section is the relativelocation of the nerves 106. FIG. 1 B illustrates the case of theherniated disc, wherein a portion of the nucleus pulposus has rupturedthrough a defect in the annulus fibrosis, resulting in a pinched nerve110. This results in pain and further complications, in many cases.

FIG. 1C illustrates the post-operative anatomy following partialdiscectomy, wherein a space 120 remains adjacent a hole or defect in theannulus fibrosis following removal of the disc material. The hole 122acts as a pathway for additional material to protrude into the nerve,resulting in the recurrence of the herniation. Since thousands ofpatients each year require surgery to treat this condition, withsubstantial implications in terms of the cost of medical treatment andhuman suffering, any solution to this problem would welcomed by themedical community.

SUMMARY OF THE INVENTION

The subject invention resides in methods and apparatus for treating discherniation, which may be defined as the escape of nucleus pulposusthrough a void or defect in the annulus fibrosis of a spinal discsituated between upper and lower vertebra. In addition to preventing therelease of natural disc materials, the invention may also be used toretain bone graft for fusion, therapeutic and artificial discreplacement materials. The invention is particularly well suited to theminimization and prevention of recurrent disc herniation, in which casethe defect is a hole or void which remains in the annulus fibrosisfollowing disc operations involving partial discectomy.

In broad, general terms, to correct defects of this type, the inventionprovides a conformable device which assumes a first shape associatedwith insertion and a second shape or expanded shape to occlude thedefect. The device may take different forms according to the invention,including solidifying gels or other liquids or semi-liquids, patchessized to cover the defect, or plugs adapted to fill the defect.

The device is preferably collapsible into some form for the purposes ofinsertion, thereby minimizing the size of the requisite incision whileavoiding delicate surrounding nerves. Such a configuration also permitsthe use of instrumentation to install the device, including, forexample, a hollow tube and a push rod to expel the device or liquefiedmaterial out of the sheath for use in occluding the disc defect.

A device according to the invention may further include one or moreanchors to assist in permanently affixing the device with respect to thedefect. For example, in the embodiment of a mesh screen, the anchors mayassume the form of peripheral hooks configured to engage with thevertebra on either side of the disc. The invention further contemplatesa distracting tool used to force the anchors into the vertebra. Such atool would preferably feature a distal head portion conformal to theexpanded shape of the device, enabling the surgeon to exert force on theoverall structure, thereby setting the anchors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross section of a human disc exhibiting normal anatomy;

FIG. 1B is a cross section used to illustrate a disc herniation;

FIG. 1C is a drawing of a disc following a partial discectomy, showinghow a space or void remains in the annulus fibrosis;

FIG. 2 is a drawing which illustrates a preferred embodiment of theinvention in the form of a flexible stent used to occlude a defect inthe annulus fibrosis to minimize recurrent disc herniation;

FIG. 3A is a drawing of an applicator used to insert the flexible meshstent embodiment of FIG. 2;

FIG. 3B shows the applicator of FIG. 3A with the stent partiallyexpelled;

FIG. 3C illustrates a fully expanded shape assumed by the device of FIG.2 following removal of the insertion tool;

FIG. 4A illustrates the addition of optional peripheral anchors aroundthe stent in the FIG. 4 to assist in fixation;

FIG. 4B is an end view of the device of FIG. 4A including the peripheralanchors;

FIG. 5 is a side-view drawing of the device of FIGS. 4A and 4B anchoredinto upper and lower vertebra bounding the herniated disc;

FIG. 6A illustrates an optional distraction tool used to set the anchorsof the device of FIGS. 4 and 5 into the vertebra;

FIG. 6B shows how the distracting tool would be inserted into the deviceto effectuate distraction;

FIG. 7A is a side-view drawing in partial cross-section illustrating theway in which notches may be made to adjoining vertebra to receive adevice according to the invention;

FIG. 7B is a drawing of a tool which may be used to form the notchesdepicted in FIG. 7A;

FIG. 7C illustrates the way in which a flexible body may be retained bythe notches described with respect to FIGS. 7A and 7B;

FIG. 8 illustrates an alternative orientation of a flexible body havinga convex surface facing outwardly with respect to the wall of the discbeing repaired;

FIG. 9A illustrates how the device according to the invention may befixed with anchors that penetrate through the disc to be captured at theouter wall thereof;

FIG. 9B illustrates an alternative use of anchors which remain withinthe body of the disc material and do not penetrate its outer wall;

FIG. 9C illustrates an alternative method of fixation, wherein boneanchors are introduced into the vertebrae on either side of the disc inneed of repair, as opposed to anchors deployed within or through thedisc itself;

FIG. 10A illustrates an alternative device according to the invention inthe form of a resilient plug;

FIG. 11A illustrates an alternative embodiment of the invention whereina coiled wire is used to occlude a disc defect;

FIG. 11B is a side-view representation of the coiled wire of FIG. 11 A;

FIG. 11C illustrates how a wire with a coiled memory shape may bestraightened and introduced using a plunger-type instrument;

FIG. 12 illustrates yet a different alternative embodiment of theinvention wherein a material in liquid or gel form may be introducedinto a defect, after which it hardens or solidifies to prevent furtherrupturing;

FIG. 13A illustrates yet a further alternative embodiment of theinvention, in the form of a stent having a plurality of leaves;

FIG. 13B illustrates the alternative of FIG. 13A, wherein the leavesassume a second shape associated with defect occlusion, preferablythrough memory affect;

FIG. 14A illustrates an aspect of the invention wherein a conformabledevice is suspended within a gel or other resilient material for defectocclusion;

FIG. 14B is a side-view drawing of the embodiment of FIG. 14A;

FIGS. 15A-15E are drawings which show various different alternativeembodiments according to the invention wherein a patch is used insideand/or outside of a void in need of occlusion;

FIG. 16A is a top-view, cross-sectional drawing of a version of theinvention utilizing posts or darts and sutures;

FIG. 16B is a side-view drawing of the embodiment of FIG. 16A;

FIG. 17A shows how posts or darts may be crisscrossed to form a barrier;

FIG. 17B is a side-view drawing of the configuration of FIG. 17A;

FIG. 18A is a side-view drawing of a barbed post that may be used forocclusion according to the invention;

FIG. 18B is an on-access view of the barbed post;

FIG. 18C illustrates how a single larger barbed post may be used fordefect occlusion;

FIG. 18D illustrates how the barbed post of FIGS. 18A and 18B may beused in plural fashion to occlude a defect;

FIG. 19A is a drawing which shows how shaped pieces may be inserted toclose off an opening;

FIG. 19B continues the progression of FIG. 19A, with the pieces beingpulled together;

FIG. 19C illustrates the pieces of FIGS. 19A and 19B in asnapped-together configuration;

FIGS. 20A-20E are a progression of drawings which show how a shaped bodymay be held into place with one or more wires to block off a defect;

FIGS. 21A-21C illustrate how wires may be used in conjunction withsnap-on beads to occlude a defect;

FIG. 22A illustrates the insertion of members adapted to receive a damcomponent;

FIG. 22B illustrates the dam of FIG. 22A locked into position;

FIG. 23A illustrates one form of defect block that accommodatescompression and distraction;

FIG. 23B shows the device of FIG. 23A in compression;

FIG. 23C shows the device of FIG. 23A in distraction;

FIG. 23D illustrates the way in which the device of FIGS. 23A-23C, andother embodiments, may be tacked into place with respect to upper andlower vertebrae;

FIG. 24A is a drawing which shows an alternative device that adjusts forcompression and distraction, in the form of a resilient dam,

FIG. 24B shows the resilient dam in compression;

FIG. 24C shows the resilient dam in distraction;

FIG. 25 illustrates a different configuration for the insertion of aresilient dam according to the invention;

FIG. 26 illustrates an alternative Z-shaped dam of resilient material;

FIG. 27A illustrates the use of interlocking fingers that permitcompression and distraction while occluding a defect;

FIG. 27B is a side-view drawing in cross-section of the configuration ofFIG. 27;

FIG. 28A illustrates an alternative interlocking finger configuration,and the way in which such members are preferably installed;

FIG. 28B shows how the first of the multiple members of FIG. 28A isinstalled;

FIG. 29A is a side-view drawing of a non-contained silicon blockingmember prior to distraction;

FIG. 29B illustrates the way in which the device of FIG. 29A deformsupon distraction;

FIG. 30A is a side-view drawing in cross-section illustrating acontained silicon structure prior to distraction;

FIG. 30B illustrates how the contained silicon structure of FIG. 30Aremains essentially the same in shape upon distraction;

FIG. 31A illustrates the use of threaded metal plug with particularapplicability to bone graft retention;

FIG. 31B illustrates a rigid plug with ridges enabling it to be impactedinto place;

FIG. 31C shows the use of asymmetric ridges to resist posteriormigration;

FIG. 31D shows how teeth, screw threads or ridges on certain plugembodiments would extent at least partially into the adjacent vertebrafor secure purchase; and

FIG. 32 illustrates bilateral plug positioning according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Having discussed the problems associated with post-operative partialdiscectomy with respect to FIGS. 1A-1C, reference will now be made toFIG. 2, which illustrates a preferred embodiment of the invention,wherein a device in the form of a stent 202 is used to occlude a defect204 in a human disc, as shown. In this preferred embodiment, the deviceis composed of a flexible material, which may be cloth, polymeric ormetallic. For reasons discussed below, a titanium mesh screen ispreferred with respect to this embodiment of the invention.

A flexible device is also preferred because the surgeon is presentedwith a very small working area. The incision through the skin istypically on the order of 1 to 1.5 inches in length, and the space atthe disc level is approximately 1 centimeter on the side. As aconsequence, the inventive device and the tools associated withinsertion and fixation described below must be sufficiently narrow tofit within these confines.

As shown in FIGS. 3A-3C, a flexible screen enables the device to becollapsed into an elongated form 302, which, in-turn, facilitatesintroduction into a sheath 304 associated with insertion. A push rod 306may then be introduced into the other end of the sheath 304, and eitherthe sheath pulled backwardly or the push rod pushed forwardly, or both,resulting in the shape shown in FIG. 3C, now suitable for implantation.

To further assist in fixation with respect to the surroundingphysiology, anchors 402 may be provided around a peripheral edge of thedevice, as shown in FIG. 4A. FIG. 4B shows an end view of the device ofFIG. 4A, and FIG. 5 illustrates the device with anchors generally at500, being fixed relative to a defective disc 504 bounded by upper andlower vertebrae at 502. It will be apparent to those of skill that eachof the devices disclosed herein may be made in different sizes, havingvarying peripheral dimensions, for example, to match differently sizeddefects.

FIGS. 6A and 6B illustrate how a distracting tool 602 may be used toforce the anchors into the vertebrae. That is, having introduced thedevice into the approximate area, the tool 602, having a forward shapecorresponding to that of the expanded mesh shape, may be introducedtherein, as shown in FIG. 6B. With force being applied to the tool 602,the anchors may be permanently set into the surrounding bone/tissue.

FIG. 7A illustrates an alternative approach to fixation, wherein one ormore notches 700 may be made into the upper and lower vertebra,preferably through the use of an air-operated drill 704 shown in FIG.7B, having a cutting wheel 702 adapted for such a purpose. FIG. 7Cillustrates the way in which a flexible body 708 may be retained by thenotches 700 described with respect to FIGS. 7A and 7B. FIG. 8illustrates an alternative orientation of a flexible body having aconvex surface facing outwardly with respect to the wall of the discbeing repaired.

FIG. 9A illustrates a further alternative associated with fixationwherein anchors 902 which penetrate the outer wall of the disc 905 areused to hold a flexible repair device 900 in place as shown. FIG. 9Bshows yet a further alternative fixation modality, wherein disc anchors906, which do not penetrate the outer wall of the disc, but, ratherremain there within, are used to hold the device 904 in place.

FIG. 9C illustrates yet a further alternative mode of fixation, whereinanchors 908 are used to hold the device to upper and lower vertebra, asopposed to the anchors of FIGS. 9A and 9B, which are used with respectto the disc. Regardless of whether fixation takes place within thevertebra or within the disc, it will be noted that according to thepreferred embodiment of the invention, both the device used to occludethe defect and the fixation means are sufficiently flexible that thedefect remains occluded with movement of the spine, that is, with thepatient leaning forwardly and backwardly which will tend to change thespacing between the upper and lower vertebra.

FIG. 10 illustrates yet a different embodiment of the invention wherein,as opposed to a piece of flexible material or mesh, a resilient plug1002 is instead utilized to occlude the disc defect. As in the case ofthe flexible sheath-like embodiments described above, such plugs arepreferably offered in different sizes to correlate with differentlysized defects.

In terms of a preferred material, a device according to the inventionwill therefore remain sufficiently flexible during movement while beingcapable of exerting continuous outward forces and withstandingrepetitive compression and distraction of millions of cycles. The devicewould, therefore, preferably be made of a material that has thesecharacteristics, while, additionally being radio-opaque for X-rayimaging, without producing too many unwanted artifacts in magneticresonance imaging. A wire mesh of titanium is therefore preferable,since this has the proper X-ray/MRI characteristics while exhibiting therequisite flexibility for the cyclic flexion and extension. With respectto the embodiment of FIG. 10, a resilient, rubber-like material may beused to occlude the defect as shown in the drawing from a side-viewperspective.

The invention is not limited in the sense that any conformable devicemay be used with a first shape permitting the device to be introducedinto the defective area and a second shape wherein the device includes adefect. As shown in FIGS. 11A-11C, for example, a wire 1102 having a“memory effect” may be used, preferably having a final diameter which islarger than void 1104. FIG. 11 B shows the coil 1102 in cross-sectionbetween upper and lower vertebra. Preferably, this embodiment would usea metal wire that may be straightened, but retain the memory of itscoiled shape. As such, the apparatus of FIG. 11C may be used tointroduce the wire in straightened form 1108 with a plunger 1110, suchthat as the wire exits at 1106, it returns to its memorized state of acoil (or alternative second shape operative to include the defect).

As yet a different alternative mode of introduction, a material may beinjected into the disc in liquid form, then allowed to hardened into asize sufficient to occlude the annular hole. As shown in FIG. 12,material 1202 may be injected into the void of the disc space using aplunger 1204 inserted into a tube 1206. Upon introduction in thismanner, the liquid would then solidify, forming a resilient plug.

Various materials may be utilized for this purpose, including variouspolymers which are caused to solidify by various means, includingthermal or optical activation, or chemical reaction as part ofmulti-part compounds. A preferred material with respect to thisembodiment would be a hydrogel. Hydrogels may be placed into the disc ina dehydrated state, and, once inside the disc, they imbibe water. Afterhydration, hydrogels have the same biomechanical properties as a naturalnucleus and, in addition, as the hydrogels swell, they become too largeto extrude back through the annular window. U.S. Pat. Nos. 5,047,055 and5,192,326 provide a listing of hydrogels, certain of which areapplicable to this invention.

An elastomer may be used as an alternative to a hydrogel or othermaterial. A number of elastomers may be suited to the invention,including a silicon elastomer, which comprises a cured dimethylsiloxanepolymer and Hexsyn, having a composition of one-hexane with three tofive percent methylhexaiene. A preformed elastomer may be inserted intothe inclusion upon curing or, alternatively, as discussed with referenceto FIG. 12, may be injected into the disc space and liquid form.Chemicals may be added to accelerate curing, as discussed above, or, ahot or cold probe, or UV light may be introduced to facilitate oraccelerate the curing process. Preferably, such materials would includea radio-opaque additive which would enable the physician to verify theposition of the implant with an X-ray. Ideally, the radio-opaqueadditive would not change the mechanical properties of the gel orelastomer, and would ideally incorporate contrast throughout to enhancedetail.

Now making to FIGS. 13 and 14, FIGS. 13A and 13B illustrate analternative type of stent having leaves or other appendages that may befolded into a compact state for insertion, FIG. 13A, and which expand,through memory affect, for example, to a state such as that shown inFIG. 13B. A stent such as this, as well as other devices disclosedherein such as the coil form of FIG. 11, may be used in conjunction witha gel or other void-filling material as described above. As shown inFIG. 14A, a stent 1402 of the type shown with respect to FIG. 13B, maybe introduced into the void, after which the remaining volume of thevoid may be filled with a material 1404 which solidifies into aresilient material. FIG. 14B is a side-view drawing of the embodiment ofFIG. 14A. An expandable stent of this kind may be incorporated into theelastomer or other resilient material to help prevent migration of theprosthesis through the annular hole. In contrast to embodiments of theinvention wherein a stent is used independently, in this particularembodiment, the stent would preferably not touch vertebra, since itwould be surrounded entirely by the elastomer or other gel material.

FIGS. 15A-15E illustrate various alternative embodiments according tothe invention wherein a patch material is used inside, outside, orpartially inside and outside of a defect to be blocked. FIG. 15Aillustrates a flat patch attached onto the outside of the disc. FIG. 15Billustrates a patch attached on the outside but wherein a centralportion extends inwardly into the void. FIG. 15C illustrates a patchdisposed within the disc to block the defect. FIG. 15D illustrates how apatch may be anchored to the bone above and below the disc, and FIG. 15Eillustrates how the patch may be anchored to the disc itself. The patchmaterial be a fiber, including natural materials, whether human,non-human or synthetic; an elastomer; plastic; or metal. If a fibermaterial is used, it may be selected so as to promote tissue in-growth.Growth of a patient's tissue into the material would assure a morepermanent closure of the annular window. The patch may be attachedwithin appropriate means, including stitches, staples, glue, screws orother special anchors.

In addition to the use of patches attached with sutures, staples orother materials, the annular defect may be closed with staples or otherdevices which attach to the annulus without the need for patch material.For example, as shown in FIG. 16A, darts 1602 may be inserted throughthe wall of the annulus 1604, then linked with sutures 1606, preferablyin woven or criss-crossed fashion, as shown in FIG. 16B. As analternative, appropriately shaped darts 1702 may be criss-crossed orotherwise interlocked to the close the annular hole, as shown in thetop-view cross-section drawing of FIG. 17A or a side-view of FIG. 17B.

The use of flexible stents as described elsewhere herein may take onother forms, as shown in FIGS. 18A-18D. The device of FIG. 18A, forexample, preferably includes a body 1802, preferably including a bluntanterior end to prevent penetration of the anterior annulus, and outerspikes 1806, preferably having different lengths, as best seen in theon-axis view of FIG. 18B. Such a stent configuration may provide moreareas of contact with the vertebral end plates, thereby decreasing thechances of stent extrusion. As shown in FIG. 18C, the longer spikes 1806are configured to bend during insertion, thereby preventing posteriorextrusion. The shorter spikes, 1806′, are sized so as not to engage thevertebrae, and therefore may be made thicker to prevent deflection bydisc material. As an option, the shorter spikes 1806′ may also be angledin the opposite direction as compared to the longer spikes 1806 toresist migration of the disc material. As yet a further option, thelonger spikes may vary in length on the same stent so as to be conformalto the vertebral end plate concavity. As shown in FIG. 18D, multiplespike stents of this kind may be inserted so as to interlock with oneanother, thereby preventing migration of the group.

As shown in FIGS. 19A-19C, shapes other than spiked stents may be usedin interlocking fashion. In FIG. 19A, a first piece 1902 is insertedhaving a removable handle 1904, after which pieces 1902′ and 1902″ areinserted, each having their own removable handles, as shown. In FIG.19B, the handles are pulled, so as to bring the pieces together, and inFIG. 19C, the handles are removed, and the pieces are either snappedtogether or, through the use of suitable material, sutured into place.FIGS. 20A-20E illustrate a different configuration of this kind, whereina body 2002 having anchor or wire-receiving apertures 2004 is insertedinto the annular hole, as shown in FIG. 20B, at which time a wire 2006is inserted through the body 2002 as shown in FIG. 20C. As shown in FIG.20D, the wire is installed sufficient to lock one portion of the bodyinto place, and this is followed with a wire on the opposite side,thereby holding the body 2002 in a stabilized manner. It will beappreciated that although multiple wires or anchors are used in thisconfiguration, bodies configured to receive more or fewer wires oranchors are also anticipated by this basic idea.

FIGS. 21A-21C illustrate a different alternative, wherein wires 2102each having a stop 2104 are first inserted through the annular window,after which blocking beads having snap-in side configurations arejournaled onto the wire across the annular hole, as shown in FIG. 21B.FIG. 21C illustrates how, having locked multiple beads onto the wire,the defect is affectively occluded. FIGS. 22A and 22B illustrate the useof a removable dam component. As shown in FIG. 22A, bodies 2202, eachhaving removable handles 2204, are first inserted on the side portionsof the defect, each member 2202 including slots, grooves or apertures2206, configured to receive a dam 2210, which may be made of a rigid orpliable material, depending upon vertebral position, the size of thedefect, and other factors. FIG. 22B illustrates the dam 2210 locked inposition.

Certain of the following embodiments illustrate how the inventionpermits the use of a flexible device which allows movement between thevertebrae yet blocks extrusion of nucleus through an annular hole ordefect. In FIG. 23A, for example, a flexible element 2302 is tacked intoposition on the upper vertebrae, as perhaps best seen in FIG. 23D,though it should be apparent that a fixation to the lower vertebrae mayalso be used. FIG. 23B illustrates how, once the member 2302 is fastenedin place, it may flex under compression, but return to a more elongatedshape in distraction, as shown in FIG. 23C. The blocking element 2302may be made from various materials, including shape-memory materials, solong as it performs the function as described herein. FIG. 24Aillustrates a different configuration, which is tacked to both the upperand lower vertebrae, and FIGS. 24B and 24C show how the device performsin compression and distraction, respectively. Since devices attached toboth the upper and lower vertebrae need not automatically assume amemorized shape, alternative materials may preferably be used, includingbiocompatible rubbers and other pliable membranes. It is important thatthe flexible member not be too redundant or stretched so as to compressthe nerve, as shown in FIG. 25. FIG. 26 illustrates an alternativeZ-shaped installation configuration.

As an alternative to inherently flexible materials which occlude adefect while accommodating compression and distraction, interleavingmembers may alternatively be used, as shown in FIGS. 27-28. FIG. 27A isa view from an oblique perspective, showing how upper and lower plate2702 and 2704 of any suitable shape, may be held together with springs2706, or other resilient material, between which there is supportedinterleaving tines 2708. As better seen in FIG. 27B, the springs 2706allow the upper and lower plates 2702 and 2704 to move toward and awayfrom one another, but at all times, tines 2708 remain interleaving,thereby serving to block a defect.

FIGS. 28A and 28B illustrate the way in which interleaving members ortines are preferably inserted directly to vertebrae. Since each memberoverlaps with the next, such tines are preferably installed from frontto back (or back to front, as the case may be), utilizing a tool such as2810, as shown in FIG. 28B. The instrument 2810 forces each tack intoone vertebrae at a time by distracting against the other vertebrae,thereby applying pressure as the jaws are forced apart, driving the tackinto the appropriate vertebrae. The tack may be held into place on theinstrument by a friction fit, and may include a barbed end so as not topull out following insertion.

As a further alternative configuration, a collapsed bag may be placedinto the disc space, then filled with a gas, liquid or gel once inposition. The bag may be empty, or may contain a stent or expandingshape to assist with formation. In the case of a gel, silicon may beintroduced so as to polymerized or solidify. As shown in FIGS. 29A and29B, the use of a non-contained silicon vessel may be used, but, underdistraction, may remain in contact with the vertebrae, therebyincreasing the likelihood of a reaction to silicone. The inventiontherefore preferably utilizes a contain structure in the case of asilicon filler, as shown in FIG. 30A, such that, upon distraction, thevessel remains essentially the same shape, thereby minimizing vertebralcontact.

It is noted that, depending upon the configuration, that the inventionmay make use of a bioabsorbable materials, that is, materials whichdissolve in the body after a predetermined period of time. For example,if darts such as those shown in FIGS. 16 and 17 are used, they maybioabsorb following sufficient time for the in-growth of recipienttissue sufficient to occlude the defect independently. Any of the otherconfigurations described herein which might not require certaincomponents in time may also take advantage of bioabsorbable materials.Furthermore, although the invention has been described in relation topreventing the release of natural disc materials, the invention may alsobe used to retain bone graft for fusion; therapeutic materials includingcultured disc cells, glycosaminoglycans, and so forth; and artificialdisc replacement materials.

Disc fusions are generally performed for degenerative disc disease,spondylolysis (a stress fracture through the vertebra),spondylolisthesis (slippage of one vertebra on another), arthritis ofthe facet joints, spinal fractures, spinal tumors, recurrent discherniations, and spinal instability. The procedure attempts to eliminatemotion between vertebra to decrease a patient's pain and/or preventfuture problems at the intervertebral level.

Devices such as spinal cages are generally used in conjunction with suchprocedures to maintain the separation between the vertebrae until fusionoccurs. Some surgeons believe that cages are not necessary to maintainthe separation, and instead use pedicle screws or hooks and rods toperform this function. Whether or not a cage is used, bone graft isgenerally introduced through a hole formed in the disc space to achievean interbody fusion.

Unfortunately, bone material placed into the disc space can extrudethrough the hole used for insertion. Bone graft extruded through a holein the posterior portion of the disc may cause nerve root impingement.The procedure to fuse vertebra across the disc space from a posteriorapproach is known as a PLIF (posterior lumbar interbody fusion). Bonecan also be placed into the disc space from an anterior approach ALIF(anterior lumbar interbody fusion). Extruded bone from an anteriorapproach would not lead to nerve impingement but could decrease thelikelihood of a successful fusion by decreasing the volume of bonegraft.

The present invention may be used to prevent the loss of the bone graftmaterial associated with fusion techniques, whether or not a cage isused. In this particular regard, however, some of the devices disclosedherein may be more suitable than others. Generally speaking, since thegoal is not to preserve disc function and motion, the stent, plug, andpatch embodiments may be more appropriate. Although the plug embodimentwould be a good choice when there is ample room in the spinal canal toallow insertion, the expandable stent design would be beneficial whenplug insertion risks nerve injury. Conversely, since the goal is tomaximize the amount of bone inserted into the disc space, theembodiments using hydrogels and elastomers might not be optimum, sincesuch materials may occupy too much space in some circumstances.

The preferred choice of materials may also be changed since motion isnot being maintained. Materials and designs with shape memory may bebeneficial. As another example, the polymer plug embodiment may changedto a metal such as titanium. A metal plug may be fabricated with threadsand screwed into place, as shown in FIG. 31A, or the device may featureridges and be impacted into place (FIG. 31B). As shown in FIG. 31C, theridges may also be asymmetric to resist posterior migration. In allcases, the teeth, screw threads or ridges would extent at leastpartially into the adjacent vertebra for secure purchase, as depicted inFIG. 31D. Such plugs may also be positioned bilaterally, that is, withtwo per level, as shown in FIG. 32.

1. A device for preventing the escape of natural, artificial, ortherapeutic material through a defective region in an annulus fibrosisof a spinal disc, and for preventing disc herniation, comprising: animplant having a first physical extent facilitating introduction of theimplant relative to the defective region in the annulus fibrosis, and apredetermined second physical extent forming a final shape of thedevice, different from the first, wherein the implant is composed ofmaterial that naturally returns to the predetermined second physicalextent and that functions to occlude the defective region by expandingfrom the first physical extent to the second physical extent, andwherein no further steps are required to form the predetermined secondphysical extent.
 2. A device according to claim 1, wherein: the implantis composed of flexible or compressible material; the first physicalextent is achieved by compacting the implant; and the second physicalextent is achieved through expansion of the implant.
 3. A deviceaccording to claim 2, wherein the implant includes a flexible screen orpatch.
 4. A device according to claim 1, further comprising one or moreanchors to hold the implant in place relative to the defective region.5. A device according to claim 1, wherein: the implant comprises aliquid or gel that solidifies to achieve the predetermined secondphysical extent.
 6. A device according to claim 5, further comprising ahydrogel or elastomer.
 7. A device according to claim 1, wherein thefirst physical extent is achieved by straightening the implant forintroduction; and the second physical extent is achieved as the implantreturns to the predetermined shape.
 8. A device according to claim 1,further comprising a plurality of implants that function collectively toachieve the second physical extent.
 9. The device according to claim 8,wherein the implants are introduced separately.
 10. A device accordingto claim 1, wherein the implant occludes the defective region whileallowing compression and distraction of the disc with respect to normalspinal movement.
 11. A device according to claim 1, wherein the implantincorporates a radio-opaque contrast material.
 12. A device according toclaim 1, wherein the implant is retained in notches in the upper andlower vertebrae.